1. Field of the Invention
The present invention relates to a wireless communications system which has wireless base stations and a wireless communication controller, and more particularly, to control of a communication path in a wireless communications system.
2. Description of the Related Art
In recent years, wireless LAN has been increasingly introduced as intranet environment. A general wireless communications system such as the wireless LAN comprises wireless base stations and a wireless communication controller. A plurality of the wireless base stations are dispersed to cover an intended area in which the wireless LAN can be utilized. Then, the wireless communication controller controls the plurality of wireless base stations.
FIG. 1 is a block diagram illustrating the configuration of a conventional radio communications system. This is a general traffic concentrated wireless communications system.
Referring to FIG. 1, this wireless communications system comprises wireless communication controller (controller: CTRL) 901, and a plurality of wireless base stations (access points: AP) 902-904. APs 902, 903 are connected to the same sub-net, while AP 904 alone is connected to another sub-net beyond router (R) 907.
APs 902-904 can accommodate wireless mobile terminals (ST) 905, 906 through wireless channels. STs 905, 906 are connected to a wired LAN through associated APs 902-904.
CTRL 901 intensively controls APs 902-904, including connections of STs 905, 906 to APs 902-904 and movements of STs 905, 906 among APs 902-904, and routing of all paths through APs 902-904. Since this system is traffic concentrated, all traffic of APs 902-904 is transferred through CTRL 901.
As another conventional wireless communications system, a system having a routing function provided in each AP has been proposed for reducing a load on CTRL.
FIG. 2 is a block diagram illustrating the configuration of another conventional wireless communications system. Unlike the one illustrated in FIG. 1, this is a traffic distributed wireless communications system.
Referring to FIG. 2, this wireless communications system comprises CTRL 911 and a plurality of APs 912-914, as is the case with the one illustrated in FIG. 1. APs 912, 913 are connected to the same sub-net, while AP 914 alone is connected to another sub-net beyond router 907.
APs 912-914 can accommodate STs 915, 916 over the air. STs 915, 916 are connected to a wired LAN through associated APs 912-914. APs 912-914 have a routing function, unlike APs 902-904 in FIG. 1. APs 912-914 can directly exchange data without intervention of CTRL 911.
CTRL 911 intensively controls APs 912-914, including connections of STs 915, 916 to APs 912-914, and movements of STs 915, 916 among APs 912-914. However, since each of APs 912-914 has the routing function, CTRL 911 need not transfer packets among APs.
Further, as a yet another conventional wireless communications system, there has been proposed a system in which AP functions as an anchor such that a communication can be continued even if ST moves between different sub-nets (see, for example, JP-A-2003-318956 (pages 2-4, FIGS. 3, 4)).
FIG. 3 is a block diagram illustrating the configuration of a yet another conventional wireless communications system. Like the one illustrated in FIG. 2, this is a traffic distributed system, where one AP functions as an anchor for movements of ST.
Referring to FIG. 3, this wireless communications system comprises CTRL 921 and a plurality of APs 922-924, as is the case with the one illustrated in FIG. 1. APs 922, 923 are connected to the same sub-net, while AP 924 alone is connected to another sub-net beyond router (R) 927.
APs 922-924 can accommodate STs 925, 926 over the air. STs 925, 926 are connected to a wired LAN through associated APs 922-924. Unlike APs 902-904 in FIG. 1, APs 922-924 have a routing function. AP 922 and AP 923 within the same sub-net can exchange data without intervention of CTRL 921.
When ST 926 moves from AP 923 to AP 924 connected to another sub-net beyond router (R) 927, AP 923 serves as an anchor to relay data without making ST 925 conscious that ST 926 has moved. In this event, AP 923 is newly connected to ST 926 through AP 924 while leaving a path between AP 923 and ST 925 through AP 922. Then, AP 923 relays a communication between ST 925 connected through AP 922 and ST 926 connected through AP 924.
CTRL 921 intensively manages APs 922-924, including connections of ST 925, 926 to APs 922-924, and movements of STs 925, 926 among APs 922-924. However, since each of APs 922-924 has the routing function, CTRL 921 need not transfers packets among subordinate APs.
However, the foregoing related art has problems as shown below.
In the conventional example of FIG. 1, since a traffic load concentrates on CTRL 901, CTRL 901 forms a bottleneck to limit the number of STs 905, 906 which can be accommodated in the system.
In the conventional example of FIG. 2, although CTRL 911 is alleviated a traffic load concentrated thereon, communications cannot be continued when STs 915, 916 move beyond router 917.
In the conventional example of FIG. 3, while ST can move beyond router 927, a communication path runs by way of an anchor, and therefore becomes longer to increase a delay in some cases. Also, AP 923 is burdened with a higher load when it serves as an anchor.